The invention relates a process for carrying out a load-dependent regulation of the brake pressure on a commercial vehicle, equipped with an electrically acting anti-lock system (ABS) and with an electronic central control and ABS brake valves located near the vehicles axles. Rotational-speed transmitters assigned to the brakeable wheels, serve as instantaneous wheel speed sensors for an ABS control which takes effect at a wheel brake pressure near the locking limit.
In modern conventional commercial-vehicle brake systems, an automatically load-dependent brake (abbreviated hereafter to ALB) is usually provided in order to allow for large rear-axle load differences between empty and loaded vehicles as efficiently as possible in braking terms.
An object of such systems is to influence the brake forces mainly on the rear axle according to the lower axle load in the event of part loading. Also, under specific preconditions the central should influence the brake forces on the front axle by a load-dependent reduction of the brake pressure set by the brake pedal and thereby to primarily counter the danger of skidding arising from over-braked rear axles. Furthermore, a reduction of the brake-pressure level under part loads is also desirable in order to ensure a finely stepped brake actuation. In air-suspension vehicles such as shown in DE-05 37 11 175, accordion pressure between tractor and trailer; and in steel suspension vehicles the axle compression travel transmitted via a linkage, or the electrical signal from a pressure-sensitive or tension-sensitive electronic load transmitter preceding a spring bearing, are all used are a measure of the input quantity indicating the axle load.
These types of systems have disadvantages. Influencing of at least one axle-specific brake-pressure regulating valve mechanically is susceptible to damage under rough operating conditions. Another disadvantage is that it is even necessary to have appropriate activating elements in diverse and often even non-uniform versions even within a vehicle model series.
A load detection system based on a transmission linkage is inaccurate for ALB control. For example, in a common brake-pressure control of the axle groups of vehicles with leading or trailing axles or with hard suspension transmission linkage controls would be inaccurate. Also such controls entail considerable costs.
It has already been proposed to regulate the brake pressures in axle terms according to the absolute wheel slip, or alternating to adjust the brake-pressure distribution so that specific wheel-slip relations between the axles are established. However, such solutions have proved unsatisfactory, because, for the lack of a reliable reference speed of non-braked wheels, the absolute wheel slips in the braked vehicle can be determined only approximately, and because of production divergences in the tires, even exactly determined slips, do not offer reliable information on actual adhesion stress.
In contrast to this, an object of the invention is to utilize tried and tested and robust components, signal paths and transmitters of an existing anti-lock braking system (abbreviated hereafter to ABS) and thereby perform an automatically load-dependent braking function, taking effect well below the locking limit. For this, the invention provides a process which also makes it possible to regulate the brake pressure and consequently the brake-force distribution well below, the locking limit, at least specifically in axle terms
With such a regulation, it is also then possible to select higher brake pressures than hitherto customary on the front axle, independently of the brake-pressure control on the rear axle. By an appropriate extension of the microprocessor program of the electronic ABS controller, there is no need for the mechanical (or, in electropneumatic brake systems, the additional electronic) wheel-load or axle-load sensors.
The process proposed by the invention thus allows a considerable simplification and increase in reliability of a load-adaptive brake system for commercial vehicles by minimizing the number of signal transmitters required and their necessary connections to an electronic control unit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.